I vaguely remember something about it being brain cancer, and the healing he got from project X experiementation essentially controlled the tumour's growth, leaving him with this mass pressing on parts of his brain causing the disjoint from reality. He occasionally has lucid periods because the tumour grows before the healing kicks in and shrinks it again.
Just what I remember hearing though

You're mostly correct, except there was a lengthy story ark that explains how he already was a hit man who would assume new identities after each mission. After one said mission he came upon a couple living in the Canadian wilderness whilst injured and delirious. He then attempted to stage the husbands death in a house fire (thus scarring himself and the husband) and assume the husbands identity and settle down. Whelp the missus came home early and he ended up accidentally killing her too, which was the last straw for his psyche. So he just sort of snapped, in fact, the husband actually survived and went on to become his main rival for like the first 30 issues. So after that mess-up he wound up at the Canadian super soldier program after discovering he had stage 4 skin cancer. Yes they tried to give him the healing factor but it went awry and horribly disfigured him. It actually took his heart getting ripped out after by the "jailer" of the place for the healing factor to kick in.

>implying snakes arnt adorable

>implying snakes arnt adorable

yes